She lets it end. No one apart from the mysterious (urg) race of aliens is trying to destroy the universe by collapsing it, they might as well be nothing, and story telling wise they're just a natural disaster without agency. She just stays in her dimensional safe box and doesn't take action. Her only actions are choosing to let things happen, but she's never the one putting them in action.

Also, the goal isn't/shouldn't be growth at all cost in a story. The axiom of Liu Cixin is his theory of "The Dark Forest", which is what it is, a literary axiom, not an universal truth.